In 1938 Cerletti used modified household current to produce a seizure for therapeutic purposes in the mentally ill. The results were dramatic, and the search for better stimuli began. The optimal stimulus would produce maximum therapeutic benefit with minimal damage. Since the seizure was generally considered to be the therapeutic factor in ECT, currents and waveforms that could produce the seizure with minimal energy were sought.
Within a decade the brief pulse and unilateral ECT techniques were described. Offner (1942) reported that the electric current passing through a living tissue does not quite follow Ohm's law. Later (1946) he postulated that the optimal stimulus would consist of exponentially rising pulses of current, about 1 ms total duration. This waveform proved difficult to produce, and in any event would have reduced the energy required by only 22% relative to move easily generated square pulses. Therefore he endorsed the use of brief square pulses. Liberson (1945) reported his pioneering work with rabbits and guinea pigs, suggested that the best stimulus rate would be between 120 and 150 pulses per second. From clinical experience (1948) he reported that stimuli of less than 0.3 ms pulse duration were unreliable, and those of more than 1 ms required more energy to produce seizures than 1 ms pulses. Friedman and Wilcox (1942) used half sine waves and unidirectional pseudogalvanic waves, inducing seizures with less energy. They also used unilateral electrode placement, resulting in substantially reduced memory impairment. Without anesthesia, however, the patients developed considerable anxiety and strongly resisted treatment, as it took sometimes several seconds before the onset of seizure. The technical limitations of electronics and the exciting psychopharmacological discoveries of the fifties reduced interest in ECT research. Woodbury et al. (1952) published animal research data favoring 50 .mu.s pulses at rates up to 300 pulses per second. However, in their recommendations for ECT instruments, they chose to disregard their own data, and they endorsed 0.5-1.0 ms pulses at a rate of 120 pulses per second, as they were easier to produce at that time. Possibly these were the reasons why the sine wave and its modifications remained the most popular waveform.
In the sixties, after the routine use of anesthesia and muscle relaxants were introduced, the search for a better stimulus was revived. Evidence was brought forward indicating that the electricity is largely responsible for the memory impairment with ECT, whereas the therapeutic effect depends only upon the seizure itself (Ottosson, 1960, 1961, 1962). Maxwell (1968) summarized the methods of increasing the effeciency of ECT stimulus in seizure induction, relating to the pulse shape, width, rate, voltage and energy. Valentine et al. (1982) studied postictal confusion and made a good case for the brief pulse current and unilateral application of ECT. Weaver et al. (1974, 1978, 1982) established that there is no advantage in exceeding 1 ms pulse width, and that there is no difference in seizure-producing potency of AC and unidirectional stimuli, Orpin (1980) described clinical experience with his own brief pulse instrument. Although he produced seizures with as little as 22 joules (as opposed to 170 joules with sine wave current), he could not demonstrate any clinical advantage. Gordon (1981, 1982) described his brief pulse machine, City University Instrument, using 1 ms stimuli, variable peak current and rate, usually 100 pulses per second. He compared it with various other modern ECT instruments (Orpins, Siemens, Theratronics, Ectron and MECTA) and the comparison favoured his own. Others (Maletzky, 1978, Christensen and Koldbaek, 1982, Malitz et al., 1982, Yudofsky, 1982), consider the MECTA machine, incorporating EEG and ECG recordings, to be the most advanced instrument.
There is no universally accepted standard at present for the specification of dose in ECT. Reasons for this are diverse. While electrical measurements are readily made with simple instrumentation, no single physical parameter has been shown to be a reliable indicator of the clinical dose when other parameters vary. This facility of measurement, however, seems to have encouraged some workers in the field to adopt dosimetry criteria inadequately calibrated with respect to quantifiable clinical effects.
Two very different electrical dosimetry criteria have been proposed in the literature. These shall first be examined for plausibility from a physical point of view. Both will then be shown to be problematic; while each is easily measured, each has important shortcomings which could possibly be overcome.
The first technique, ergometry, measures ECT dose in joules of generated electrical energy applied to electrodes. This is done by multiplying the applied voltage (V) by the current (l) and the duration of the current (t). The energy (W) applied during ECT is given by the simple formula EQU W=Vlt
If practical units are employed (volts, amperes and seconds, respectively, for V, l, and t) the energy, and thus the ergometric dose, will be in joules. With ECT instruments the voltage and the current vary during stimulus application, and a somewhat more difficult technique, called Digital Data Acquisition and Processing (DDAP) is required to measure the ergometric dose according to formula: EQU W=.intg.V(t)l(t)dt
The use of ergometry as the measure of the energy deposited in the brain is unsatisfactory for other reasons too. Skin and skull electrical resistance varies a great deal even in the same individual, depending on such factors as emotions, skin preparation, and electrode placement. The ergometric dose required to deposit a given energy in the brain will vary accordingly.
The second technique, coulometry, determines ECT dose in terms of total charge which flows during the treatment. As Gordon (1981) pointed out, the use of ergometry can be very misleading. He suggests using coulometry instead. This technique is readily applicable by users of constant current instruments. The coulometric dose, Q, is given by the formula: EQU Q=lt
for steady current, and by the formula: EQU Q=.intg.ldt
for varying current. If practical units are employed, Q will be in coulombs, which are units of electric charge. Moreover, symmetric stimuli, for which the net charge is zero, such as sine waves, do indeed induce convulsions. Gordon (1981) recognized that coulometry was inadequate to specify dose, and he recommended recording and specifying peak current and ergometric dose as well.
More problems are to be encountered by those trying to conceptualize and quantify the electrical energy that may damage the brain. The living brain constantly generates electrical energy (demonstrable by EEG) and absorbs it without any harm. In order to cause any harm, the electrical energy must be deposited in the tissue at a rate which exceeds the capacity of the tissue to absorb it harmlessly. The electrical stimulus may be excessive with respect to energy, time, and space factors involved. The harmful role of energy is probably straightforward--the more energy, the more likely damage will ensue, providing other factors are constant. The role of time is twofold--if the current and tissue volume remain constant, the longer the time, the more likely is the damage. However, if the energy remains constant, the longer time it is applied, the less likely it is to cause damage. For example, 1 W applied to 1 kg of living tissue for 10 days will hardly even raise its temperature, although the energy will be 864,000 J. The same energy applied in 20 minutes with the power of 720 W (the power of a kitchen stove plate) will certainly damage the tissue.
Similarly, the role of space is twofold. The smaller the tissue volume in which a given energy is deposited, the more likely damage will occur (higher energy density). The larger the volume of tissue affected, the more likely the damage will be significant.
Power itself is not a meaningful measure of the dose, as for example 100 V applied for 1 sec. will give the same power, but much smaller dose if applied for 0.1 sec. only.
Evidently energy, power, or charge are not satisfactory single criteria of the electrostimulatory dose, and ECT dosimetry will require further refinement. (Footnote 2.) This issue will be addressed again in the discussion.